3$\times$3 Slot waveguide crossing based on Maxwell's fisheye lens

Intersection of two or more silicon slot waveguides is inevitable in modern optical integrated circuits based on silicon on insulator (SOI) platform. In this article, we design a Maxwell's fisheye lens as the crossing medium for three Si slot waveguides and numerically investigate its characteristics such as insertion loss, crosstalk and bandwidth. For the 3$\times$3 slot waveguide crossing, the average insertion loss of 1.2 dB and crosstalk levels lower than -15.1 dB are achieved in an ultra-wideband wavelength range of 415 nm covering the entire O, E, S, C, L, and U bands of optical communications. The footprint of the 3$\times$3 silicon slot waveguide crossing presented in this article is merely 2$\times$2 $\mu m^2$ which is considerably smaller compared to the previously designed Si slot waveguide crossings even with fewer number of ports. The proposed design can be expanded to support the intersection of more slot waveguides.